HYDE PARK, N.Y. Franklin D. Roosevelt had the good fortune of Hitler declaring war on the United States just four days after Pearl Harbor. With war blazing across front pages from coast to coast and the radio crackling with cries of fear and loathing, America was galvanized. Army and Navy recruiting offices were swamped by eager young men.

The jihadists of ISIS are the Nazis of 2014. Their beheading of two Americans, mocking civilization by doing it on videotape, was the rough equivalent of Hitler's declaration of war. Public opinion turned on the proverbial dime, setting the stage for President Obama's speech Wednesday night, just hours before our commemoration of the 9/11 terrorist attack in 2001. America had been persuaded that the Islamic State, also called ISIS, was dangerous, evil and determined to prevail, and nearly everyone was puzzled and angry that the president took so long to do anything about it.

Nobody would confuse Barack Obama with FDR, and he understands now that he pulled a boner describing the Islamic State as "the junior varsity." Nevertheless, he still preferred to lie than own up to what he had said, telling Chuck Todd on "Meet the Press" that he wasn't really talking about ISIS when he said that. But in his speech, he showed that he's willing now to treat ISIS as the varsity, America's vilest enemy since 1941. We note the change in his rhetorical resolve to "degrade and ultimately destroy" the Islamic State.

Mr. Obama is not the first president to wrap his rhetoric around a world he wants instead of the world as he finds it. Woodrow Wilson, an idealist and pacifist, wanted desperately to keep the United States out of World War I. He agreed to declare war when there was nothing else he could do. He won resounding applause when he asked Congress for the declaration, and his secretary, Joseph Tumulty, said the president returned to the White House and put his head on his hand and wept uncontrollably.

"The Buck Stops Here," a book by Thomas Craughwell and Edwin Kiester, details some of the toughest presidential decisions and is prominently displayed in the bookstore here in Hyde Park at the Franklin D. Roosevelt Presidential Library and Museum. The authors illustrate how pressure on presidents can cause them to radically change their minds and the underpinnings of foreign policy. They take the title from Harry S. Truman's guiding maxim, displayed boldly on his desk in the Oval Office. George W. Bush, reflecting the verbose language of a later age, said it without the punch: "Under our system, I'm the decider. I hear all the voices and read all the opinions, and then I decide."

Mr. Obama has always squirmed in the position of the Great Decider of foreign policy, reflecting the inexperience of a younger man who arrived at the White House with little more than "community organizer" on his resume. He has yet to accept responsibility for the decisions at Benghazi, where Chris Stevens, the American ambassador and three other Americans were killed by Islamists. The admission that he had no strategy to eliminate ISIS was not a slip of the tongue, but a slip of the facts.

But he knows his dithering time is over because ISIS has a strategy, and it's a scary one. "For the first time since 9/11, a determined and capable enemy has the space and security to plan complex, long-range operations," Ryan Crocker, former ambassador to Iraq and Syria, writes in The Wall Street Journal. It's no longer about whether Obama is capable of fighting a war against terror, but whether he can win it.

Reading public opinion, the president realized that his fellow Americans were way ahead of him and his newly announced strategy in Iraq and for Syria, to hunt, hurt and destroy ISIS and seize their considerable assets — wherever they are, with whatever economic, political and military tools he needs —makes sense. Polls immediately before his speech showed that 71 percent of Americans support bombing ISIS in Iraq, and 65 percent for bombing in Syria. Asked whether they feel safer today than they did six years ago, large majorities said no.

The president looks a lot like Charlie Chaplin in "Modern Times," who turns a corner on a stroll and finds himself leading a crowd of protesters. The flag he waves is one he found warning pedestrians to beware of an obstacle in the street ahead.

The obstacles the president has to confront in a world that won't behave were not the ones he anticipated in his second term; he campaigned as the man who had put the terrorists on the run. In his new book, "World Order," Henry Kissinger asks, "Are we facing a period in which forces beyond the restraints of any order determine the future?" It's the crucial question, and Barack Obama, while moving in the right direction, still has a long way to go to reassure us.